Surgical instruments are known in the prior art that are inserted into body cavities, such as urethras, rectum, vagina and uterus, throat, etc., to grip, tear or slice tissue samples from the particular anatomy of interest. These instruments have a jaw portion at a distal end. The jaws, or one of them, moves about a hinge and are activated by a rod reciprocating in a tubular body or other support. Often, tissue becomes entrapped in the hinge area and can cause several problems. When entrapped in the hinge area, the performance of the instrument can be adversely affected during the procedure. If the entrapped tissue is not simply loose tissue, the instrument can become lodged and must be pulled free, with resultant unintended wounding of the anatomy. Subsequent to the procedure, the instrument, which is intended to be durable and reusable, is meant to be cleaned and sterilized. Entrapped tissue becomes a major cleaning problem.
In addition, many of these instruments are electrocauterizing instruments which employ an electrical current to cauterize and staunch the flow of blood resulting from the insulted tissue affected by the maneuver. The body mounting the hinged jaws at its distal end is formed of a dielectric material in these electrosurgical instruments. A common complaint of such electrosurgical instruments is inadvertent electrical burns upon the anatomy of the patient. Such instruments are typically insulated with a dielectric material to within an inch or so of the distal portion of the device. The insulation does not extend farther because the jaws must be allowed to move freely and have to be cleaned and sterilized between procedures. However, with so much of the distal portion of the device exposed, it becomes more difficult for the surgeon to control the exact site of electrocoagulation, creating a risk of inadvertent patient burns since electrical current follows the path of least resistance, which may not necessarily be through the cauterizing tip of the instrument.
The use of sleeves at the tips of electrosurgical devices is illustrated in U.S. Pat. Nos. 4,834,095; 4,719,914; 4,076,028; and 3,920,021. These sleeves are permanently fixed to the instrument and do not require radial flexibility to serve their intended purpose. Spreader devices for various applications are illustrated in U.S. Pat. Nos. 2,447,474; 4,370,979; 4,921,423; and 509,226.
Accordingly, it is an object of this invention to provide a sheath for a surgical instrument in which a distal portion which radially expands is covered during the surgical manipulation to prevent entrapment of tissue.
It further is an object of this invention to provide an electrosurgical instrument in which the risk of inadvertent patient burn is reduced.